Various mobile devices have keys for receiving user input such as text, numbers or user commands. Such keys often contain a legend printed on a key cap, as in a wired or wireless telephone or Personal Digital Assistant (PDA) device. It is very common to illuminate such legends, particularly for mobile communication devices, by forming a key cap at least partly of a light conductive material and providing an illuminator behind the key cap so that an associated legend can be seen even without any ambient light. For instance, Nokia™ 6110 mobile telephone contained a key mat, which formed all the key caps to a telephone keypad. The key mat was made of a light conducting rubber or plastics and coated with black relatively opaque material that was then cut by a laser to form the necessary legends to the keys, hence forming white legends on black background. These legends contained the digits, alphabets and the asterisk and hatch signs. Nokia™ 5110 mobile telephone also had a light conducting key mat, but instead of carving to an opaque key surface, opaque material was deposited on the key surface to form the legends, hence providing black legends on a white background.